1. Field of the Invention
This disclosure relates in general to magnetic storage systems, and more particularly to a method and apparatus for providing a reverse air bearing surface head with trailing shield design for perpendicular recording.
2. Description of Related Art
Disk drives are used as primary data storage devices in modern computer systems and networks. A typical disk drive comprises one or more rigid magnetizable storage disks, which are rotated by a spindle motor at a high speed. An array of read/write heads transfer data between tracks of the disks and a host computer. The heads are mounted to an actuator assembly that is positioned so as to place a particular head adjacent the desired track.
Information is written on each disk in a plurality of concentric tracks by a transducer assembly mounted on an actuator arm. Typically, the transducer assembly is suspended over the disk from the actuator arm in a slider assembly, which includes air bearing surfaces designed to interact with a thin layer of moving air generated by the rotation of the disks. Transducer assemblies are said to “fly” over the disk surface as the disk rotates. To access tracks on the disk, the actuator arm moves in an arc across the disk. The physical distance between the nominal centers of two adjacent tracks is referred to as the “track pitch”. The track pitch and linear track density define the storage capacity of the disk.
Each of the disks is coated with a magnetizable medium wherein the data is retained as a series of magnetic domains of selected orientation. The data are imparted to the data disk by a write element of the corresponding head. The data thus stored to the disk are subsequently detected by a read element of the head. Although a variety of head constructions have been utilized historically, magneto-resistive (MR) heads are typically used in present generation disk drives. An MR head writer uses a thin-film inductive coil arranged about a ferromagnetic core having a write gap. As write currents are passed through the coil, a magnetic write field is established emanating magnetic flux lines from the core and fringing across the write gap. The flux lines extend into the magnetizable medium to establish magnetization vectors in selected directions, or polarities, along the track on the data disk. Magnetic flux transitions are established at boundaries between adjacent magnetization vectors of opposite polarities.
To write a computer file to disk, the disk drive receives the file from the host computer in the form of input data that are buffered by an interface circuit. A write channel encodes and serializes the data to generate a data input stream that can be represented as a square-wave type signal of various lengths between rising and falling signal transitions.
A write driver circuit uses the data input stream to generate a write current which is applied to the write head, creating the magnetic write field that writes the encoded data to the magnetizable medium of the selected disk. The write current both reverses the polarity of the magnetic write field, creating the magnetic flux transitions, and sustains a given polarity between successive magnetic flux transitions.
A write head typically employs two ferromagnetic poles capable of carrying flux signals for the purpose of writing the magnetic impressions into the track of a magnetic disk or tape. The poles are fabricated on a slider with the pole tips located at the air bearing surface. Processing circuitry digitally energizes the write coil that induces flux signals into the poles. The flux signals bridge across the write gap at the air bearing surface so as to write the magnetic information into the track of the rotating disk. The thinner the thickness of the write gap layer, the greater the number of bits the write head can write into the track.
A write head is typically rated by its areal density that is a product of its linear bit density and its track width density. The linear bit density is the number of bits that can be written per linear inch along the track of the rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). As discussed hereinabove, the linear bit density depends upon the thickness of the write gap layer. The track width density is directly dependent upon the width of the second pole tip at the ABS. Efforts over the years to increase the areal density of write heads have resulted in computer storage capacities increasing from kilobytes to megabytes to gigabytes.
For the past 40 years, longitudinal recording has been used to record information on a disc drive. In longitudinal recording, the magnetization in the bits on a disc is flipped between lying parallel and anti-parallel to the direction in which the head is moving relative to the disc.
In longitudinal recording, the magnetic medium on the disc is magnetized parallel to the surface of the disc. In perpendicular recording, however, the medium is magnetized perpendicular to the surface of the disc. According to perpendicular magnetic recording, a recording (write) magnetic field generated from a main pole of the head forms a magnetic path in which the magnetic field is induced to the underlayer disposed on the rear of the recording magnetic layer and returned from an auxiliary pole to the recording head. By switching the direction of recording magnetic field, the recording magnetic layer is magnetized in two directions towards the thickness of the medium in correspondence with the recording information code, thereby storing information. In such recording, an intensive and steep perpendicular recording (write) magnetic field can be applied to the recording magnetic layer, so that high-resolution information storage can be achieved. Moreover, when magnetized recording information is reproduced from the perpendicular magnetic recording medium recording the information, as described above, by the high-sensitive MR reproducing head using the MR device, a reproduced signal from the head has a rectangular-shaped signal waveform corresponding to the magnetized recording pattern which is sensed immediately by the head.
However, increasing areal densities to allow greater capacities is no small task. Today it is becoming more challenging to increase areal densities in longitudinal recording. Longitudinal magnetic recording is projected to be limited by the superparamagnetic limit at recording densities range between 80 to 200 Gbit/in2. To go to even higher areal densities, researchers are looking at several alternatives, including perpendicular recording. In recent years, the increased demand for higher data rate and areal density has correspondingly fueled the perpendicular head design to scale toward smaller dimensions and the need for constant exploration of new head designs, materials, and practical fabrication methods. Current exploratory head designs focus on developing a manufacturable fabrication process that uses similar design, materials, and existing tooling to ease the conversion from longitudinal to perpendicular recording to achieve ultra-high density. This aim has resulted in an effort to evaluate the current longitudinal head and consider approaches to modify its design for perpendicular recording.
Preliminary experimental evidence on head performance test on improved perpendicular media with high coercivity and tight switching field distribution indicate poor media saturation under the write pole when recording with the trailing edge of the write pole whereas substantial improvements are observed when recording is done on the leading edge. Lessons from these observations and the design of special reverse air bearing surface (ABS) suspension enable the longitudinal head to be suspended on reverse ABS, and flown them backward at zero skew. Results from flying longitudinal head backward (recording on leading edge) show improvements such as an increase in signal to noise ratio by 4-5 dB, a decrease in media transition noise by 30-50%, and elimination of poorly saturated media under the write pole. These improvements can be explained by looking at the flux path.
For a conventional single pole writer, the flux path is from the trailing edge of the write pole to the soft underlayer of the media and back to the return pole. The flux path takes the path of lowest reluctance and in this case it is the return pole. When the head is flown backward on special reverse ABS suspension, the flux is from the leading edge of the write pole to the soft underlayer of the recording media and back to the return pole. The major advantage observed from flying longitudinal head backward are mostly due to the improvement in write field gradient by the write pole's close proximity to the return pole and the direction of motion of the media in this design.
Using a conventional longitudinal head design and flying it backward for perpendicular recording requires designing a reverse ABS suspension and the development of an inverted bevel write pole fabrication to handle skew if a modified actuator arm adjusted for skew is not implemented.
It can be seen then that there is a need for a method and apparatus for providing a reverse air bearing surface head with trailing shield design for perpendicular recording.